The present invention relates to a radio access point testing method and testing apparatus, and more particularly to a radio access point testing method and testing apparatus which permit the radio characteristics test of a radio access point apparatus in a mobile communication system by remote manipulation from an operation center.
Nowadays, mobile communication terminals have become smaller in size and lower in price with the miniaturizations of components, and the number of the users of the mobile communication terminals, such as portable telephones and personal handy system (PHS) telephones, have increased explosively. With the increase in the number of the users, enhancement in convenience has been more required of each system, and the enlargement of a service area and the rise of a data transmission rate have been furthered. The stability of the system is one of important factors for the convenience of the users. For the purpose of stably operating the system, it is important to prevent the occurrence of any failure leading to system shutdown, and simultaneously to quickly detect any failure having occurred and resume system operations.
The mobile communication system has a large service area divided into a large number of small areas called “cells”, and includes radio access point apparatuses arranged in the respective cells. The radio access point apparatuses are connected to a network, and a user access terminal communicates through a radio channel with the radio access point apparatus of the cell to which the access terminal belongs, whereby it is permitted to communicate with another access terminal connected to the network.
Regarding failure detection means for the system, the failure of especially the radio interface portion of the radio access point apparatus is difficult of detection because of the uncertain interface of the very radio channel. By way of example, in a case where the antenna of the radio access point apparatus has damaged, it is difficult to immediately judge the damage as the failure of the radio access point apparatus, even at the cutoff of the communication with the user access terminal. On this occasion, such various causes are considered that the particular user will not actually exist in the cell, and that an interference wave will exist in a radio zone connected with the user access terminal, to make the communication impossible.
Means for detecting, for example, an antenna failure is disclosed as a first prior-art example for detecting the failure of the radio access point apparatus (refer to, for example, Patent Document 1: JP-A-5-14291). The antenna failure detector disclosed in Patent Document 1. is shown in FIG. 13. Referring to the figure, the output signal of the power amplifier 1 of a transmitter is passed through a directional coupler 2 as well as a circulator 3 and is transmitted from an antenna 4. Part of the output signal of the power amplifier 1 is inputted from the coupling node of the directional coupler 2 to a first detector 5, thereby to be converted into a detection voltage. A second detector 6 is connected to the node of the circulator 3 other than the nodes thereof connected to the constituents 2 and 4, and it converts reflection power from the antenna 4 into a detection voltage. The detection voltages outputted from the respective detectors are converted into a differential voltage by a subtractor 7, and the differential voltage is inputted to a comparator 8 so as to be compared with a reference voltage. The prior-art example is means for giving an alarm with the reference voltage of the comparator 8 as a threshold voltage, thereby to permit the failure detection of the antenna 4. More specifically, in a case where the antenna 4 has damaged, a voltage surface wave ratio (VSWR) degrades to increase the reflection power from the antenna 4, and hence, the difference between the detection voltages of the detectors 5 and 6 changes. When the relationship between the magnitudes of the detection voltage difference and the reference voltage being the threshold voltage has been inverted, the output of the comparator 8 changes, and the failure of the antenna 4 can be detected. Recently, a product in which the same functions as in the above are modularized is available, and the antenna failure detection is possible.
With the first prior-art example explained above, the antenna failure can be detected, but receiver defects cannot be detected. Another problem is that, in case of a reception-only antenna or the like, an antenna failure cannot be detected.
A testing method and apparatus are disclosed as a second prior-art example for permitting tests which cover even the normalities of an access point apparatus and a network. Herein, the access point apparatus and the network are tested in such a way that test information, which is transmitted by a radio channel through the network and an access point from an operation center connected to the network including the radio access point apparatus, is received by the testing apparatus (mobile access terminal) (refer to, for example, Patent Document 2: JP-A-2000-332674 and Patent Document 3: JP-A-2002-271280).
The testing apparatus disclosed in Patent Document 2 is shown in FIG. 14. Referring to the figure, a maintenance engineer in an operation center dials from a fixed telephone set 20 the telephone number of a portable telephone 19 which is connected with an access-point radio apparatus 17 to-be-tested. A call reception sequence is executed between the access-point radio apparatus 17 and the portable telephone 19, whereby the line of the fixed telephone set 20 is connected with the portable telephone 19 having an automatic offhook function. The portable telephone 19 plays back a stored vocal message after automatic offhook, and the maintenance engineer listens to the vocal message at the handset of the fixed telephone set 20. After the maintenance engineer has listened to the played-back message, he/she transmits voice from the fixed telephone set 20, and the portable telephone 19 records the voice. Besides, the maintenance engineer transmits a predetermined PB signal from the fixed telephone set 9. Upon receiving the PB signal, the portable telephone 19 plays back and transmits the recorded voice, to which the maintenance engineer can listen at the fixed telephone set 20.
If the access-point radio apparatus 17 is normal, both the vocal message stored in the portable telephone 19 and the maintenance engineer's voice recorded and played back by the portable telephone 19 can be heard. However, in a case where a radio reverse link has any abnormality, the maintenance engineer cannot hear the recorded voice. Also, in a case where a radio forward link has any abnormality, he/she cannot hear the vocal message. The prior-art example permits the normality test for the access-point radio apparatus in the above way. Besides, Patent Document 3 contains a testing method similar to that of Patent Document 2 as is expanded to a normality verifying method for a packet-data call processing function.
With the second prior-art example explained above, the normality of the access-point radio apparatus can be verified, but an antenna failure cannot be detected. Another problem is that the verifiable normality is merely the propriety of communication, and that a radio characteristics change, such as the degradation of a reception performance attendant upon a failure of slight degree, cannot be quantitatively decided.
A third prior-art example for quantitatively deciding radio characteristics is a technique wherein any abnormal part in a receiver within a radio access point apparatus is judged from electric power (refer to, for example, Patent Document 4: JP-A-11-154903). Patent Document 4, however, contains nothing about a normality test for communication and discloses an abnormality detecting method for the receiver.
As stated above, it is an actual situation that a decisive comprehensive testing method which covers the antenna failure detection to the access-point radio performance test, and a decisive testing apparatus which serves to realize them, have not been available as the testing method for the radio access point apparatus and the failure detection means.
When the radius of each individual cell is set at about 2 km, the mobile communication system requires about 10,000 access point apparatuses in order to offer a communication service over, for example, the whole of Japan. The bestowal of redundant setups on all the access point apparatuses increases a system constructing cost, and drastically spoils economy. Nevertheless, when the service is interrupted by any failure, a service quality lowers for users, and also a business company offering the service suffers the drawback of being incapable of accounting, so that the service interruption ascribable to the occurrence of the failure must be avoided to the utmost. Accordingly, inexpensive means adapted for the preventive maintenance of the system against failures is eagerly requested. Since, however, the interface between user access terminals and a radio access point is a radio channel in the mobile communication system, a communication quality changes depending upon an environment which surrounds a mobile access point or a fixed access point, and it is very difficult to decide whether an inferior communication quality is ascribable to the apparatus failure or the surrounding environment.
Now, the reasons why the failure detection of the radio access point apparatus is difficult will be concretely explained by taking as an example a case where an access point which steadily has a small number of connected access terminals is existent.
The phenomenon that the number of connected access terminals is steadily small, can sufficiently take place even when the radio access point apparatus is normal. It arises in a case, for example, where the radio access point of another system exists in the neighborhood of the radio access point apparatus. When an interference wave from the radio access point of the other system is inputted, it becomes difficult to detect a reception signal from the mobile access terminal of the pertinent system. This situation is equivalent to the reduction of the area of forward links, and the number of connectable access terminals decreases.
On the other hand, the phenomenon is considered to be ascribable to the failure of the radio access point apparatus. Examples of the failure of the radio access point apparatus will be enumerated below.
The first failure example is an antenna failure. It is considered that signal power from the access point as is received by access terminals, and signal power from the access terminals as is received by the access point will have lowered drastically, resulting in the reduction of a communicable area and the decrease of the number of connected access terminals.
The second failure example is a receiver failure. By way of example, when one receiver has undergone the failure in an access terminal which implements diversity reception by installing a plurality of receivers, a reception performance degrades. It is accordingly considered that the area of forward links has been reduced to decrease the number of connected access terminals.
The third failure example is a transmitter failure. It is considered that the signal quality of reverse links will have degraded due to the transmitter failure of the access point, and that access terminals will communicate with the neighboring access point of good signal quality, resulting in the decrease of the number of connected access terminals.
In this manner, in the mobile communication system, the same phenomena as in the failure occurrences (for example, the small number of connected access terminals) may highly possibly be observed in spite of the normal operation of the system itself, and various causes are considered for the failures, so that the failure detection is very difficult.
When it is intended to detect the above failure examples by the prior-art failure detection means, problems as stated below are involved.
With the technique which is contained in Patent Document 1 cited as the first prior-art example, the first failure example is detectable, but the cases caused by the other failure examples are undetectable. Besides, it is the propriety of communication that can be verified in the technique which is contained in Patent Documents 2 and 3 cited as the second prior-art example. Accordingly, this technique cannot detect the case of a failure which permits the communication, but which degrades the radio quality, as in the above failure example. Further, the technique which is contained in Patent Document 4 cited as the third prior-art example cannot detect the first failure example and the third failure example. Moreover, since only the decision based on the power is rendered, even the receiver failure being the second failure example cannot be detected in the case of, for example, a reception quality degradation ascribable to a phase characteristics degradation.
As thus far explained, it is the actual situation that comprehensive techniques are not available as the failure detection means and testing method for the radio access point apparatus. For the purpose of correctly estimating failure contents, it is desired to comprehensively test various failures supposed. However, the interruption of the service for the test is the lowering of serviceability as viewed from the users and must be avoided to the utmost. Besides, in the mobile communication system, especially in a portable telephone system of CDMA format wherein communication is held by finely controlling the transmission power of each mobile access terminal, the characteristics degradation of the radio access point incurs increase in the transmission power of the mobile access terminal and leads to the lowering of serviceability as shortens a communicable time period. It is accordingly important for the stable operation of the system and the enhancement of serviceability to monitor, not only the propriety of communication, but also the radio characteristics degradation. In view of these points, means is eagerly requested for testing radio characteristics on-line without interrupting the offered communication service.